It seems that I have two "private keys" on one account. Does this mean that I can use both addresses to make transactions or do I have to use the latest one (Sorry if this is a dumb question; I'm new to Bitcoin)? If I require the latest, then the 1CEN3RY address is that.

Do I have to reply per retweet or do you just read the notifications on Twitter (Equally dumb question)? I'm assuming the latter.